Devices called side pocket mandrels have been used for many years in the production of oil wells where formation fluids are brought up to the surface by an artificial lift technique known as "gas lift". To employ this technique, a gas is pumped into the tubing-casing annulus and enters the bore of the tubing downhole via a gas lift valve that is positioned within the belly of a side pocket mandrel. The gas mixes with the formation fluids in the tubing and lightens the weight of the fluid column so that the natural bottom-hole pressure of the well is sufficient to force the fluids out of the top of the tubing in an artesian manner. Typically the lift gas is recovered at the surface in a separator, and then reinjected into the annulus.
A side-pocket mandrel that has become very common in the industry is the design offered by Camco, Inc., Houston, Tex. This device has an internal side pocket that is laterally offset from the open bore therethrough, and the pocket has upper and lower, spaced-apart polish bores which receive the spaced packing assemblies on a gas lift valve. The side pocket body usually is a finished assembly that is welded into a window cut out of the side of the mandrel. To prevent other well devices that might be lowered through the tubing from hanging up on the pocket, a deflector-guide assembly also is welded into a window cut out of the mandrel above the side pocket. An example of a mandrel of this construction may be seen in FIG. 2 of U.S. Pat. No. 3,741,299, issued June 26, 1973.
The resulting mandrel design of the type described is a very lengthy and expensive assembly that incorporates a number of vertical and transverse welds which have been sources of failure, particularly when the mandrel is subjected to high burst or collapse pressures. Such welds also substantially increase manufacturing cost and consumer price. The use of an internal pocket totally enclosed within the mandrel body also results in a lengthy and expensive mandrel, and produces operational problems in using a kickover tool to set or remove gas lift valves.
The general object of the present invention is to provide a new and improved side pocket mandrel having a construction which obviates the above-mentioned problems.
Another object of the present invention is to provide a new and improved side pocket mandrel having a valve seating section of the same transverse dimension as the main body of the mandrel to strengthen the same while substantially reducing the overall length and manufacturing cost of the mandrel.
Another object of the present invention is to provide a new and improved side pocket mandrel having a short-length seating section welded therein which receives and latches a gas lift valve, and which protects the latch from being hit by other well devices.